<html>
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var a='89';
        a++;//90
        var b='ab';
        b++;//NaN
        var c=false;
        c++;//1
        var d=2.3;
        d++;//3.3
        console.log(a,b,c,d)
    </script>
</body>
</html>